Reference Manual
748384-C
September 2003
Rosemount Analytical Inc. A Division of Emerson Process Management
Introduction 1-37
NGA2000 Reference
1-20 NETWORK ISSUES
NGA analyzers operate over a digital network
called the LON. All of the internal data is avail-
able over this network.
It is possible to access this information directly
using appropriate hardware and software, but to
do so requires a certain amount of software ef-
fort. To avoid this, and to accommodate users
with investment in other protocols, several
methods of retrieving this information and allow-
ing control and configuration of the analyzers di-
rectly have been included.
a. LON
Data
Data is sent over the LON as discrete pack-
ets called "Variables". These correspond
with normal programming variables, except
that they are available to anything on the
LON capable of reading them.
There are also other packets of information
used by the NGA system, but these are not
accessible to non-NGA devices.
LON variables may be of four basic types,
floating point, integer, enumerated or string.
In addition, all but string variables may be
packaged into arrays, with a maximum of
seven floating point numbers per array, or
ten integer or enumerated types per array.
Integer
A number between 0 and 65535, expressed
as a 16-bit number. There can be up to 10
integer variables in an array.
Floating point
A four byte IEEE floating point number (in
Motorola format). This is a number that can
take a very wide range of values, but pro-
vides only about seven digits of precision.
The analyzer main reading is expressed as
a floating point number. There can be up to
7 floating point variables in an array.
Enumerated
An integer number whose value corre-
sponds to a phrase. These are used to ex-
press one of several possibilities. A typical
example is the variable that determines
whether or not a linearizer is enabled: a
value in the variable of 0 is translated as
DISABLED, while a value of 1 is translated
as ENABLED. There can be up to 10 enu-
merated variables packaged in an array.
String
A string variable contains up to 31 charac-
ters of ASCII. These are numbers which re-
fer to the standard letters, numbers and odd
symbols in the ASCII character set. There
are in general no restrictions on the sym-
bols contained in a string variable, except
that the DDE server may not work correctly
if analyzer TAG variables contain symbols
other than the alphanumeric set. There are
no string arrays.
b. LON
Data
Details
See Section 2 for details.
